The present invention relates to a cut and seal unit for sheet material.
More specifically, the present invention may be used to advantage in the food packing industry, to which the following description refers purely by way of example.
In the food packing industry, so-called "form, fill and seal" packaging machines are used wherein an orderly succession of products, equally spaced inside a tubular package, is fed continuously along a path extending through a cut and seal station equipped with a cut and seal unit for transversely cutting and sealing the tubular package to form a succession of airtight pillow packs, each containing a respective product.
The cut and seal unit normally comprises at least two cut and seal tools movable along respective annular trajectories on either side of the path of the tubular package, and which cooperate cyclically with each other to cut and seal the tubular package; and, for each tool, a respective actuating device for moving the respective tool along the respective annular trajectory independently from the other actuating device.
More specifically, each actuating device is normally defined by a cam-tappet device comprising an annular cam, and a tappet roller positively engaging the cam and connected to the respective tool to move the tool along the respective trajectory and through the cut and seal station in time with the other tool.
Though fairly effective, the above known cut and seal unit involves several drawbacks impairing both reliability and performance of the unit. That is, friction between the tappet rollers and respective cams prevents the attainment of high steady-state operating speeds; friction-induced wear of the mechanical components and the different response to such wear by the two cam-tappet devices eventually result in differing operation of the tools and a gradual reduction in cut and seal precision and quality; and, finally, high operating speeds are also prevented by the high degree of acceleration and inertia of the unit itself.